How to keep your Google packer source image version up-to-date

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When building custom images for Google Cloud Platform using Hashicorp Packer, you either specify a fixed, or latest for the Google source image version. When specifying a fixed version, you run the risk of building with a deprecated image. If you use latest, your build may introduce changes unknowingly. As we adhere to the principle to keep everything under version control, we created a utility which ensures that your packer template is always referring to the latest, explicit version of an image.

When creating a Google cloud platform virtual machine image, you either specify the exact source_image or you specify the source_image_family. The source_image pins your custom image to a specific version, whereas the source_image_family refers to the latest image version.

This utility will update the source_image in the Packer template to match the latest version of the source_image_family. In this way, the build process becomes reliable. It will specify the exact version the image is built on and will update it when a new version is available.

How does it work?

It is pretty simple. You just need a packer template as show below:

{
  "builders": [
    {
      "project_id": "my-project",
      "source_image_family": "ubuntu-1804-lts",
      "type": "googlecompute"
    }
  ]
}

To update it to the latest version, type:

$ gcp-hashicorp-packer-updater -filename tests/source-image-family.json
2021/04/11 11:31:23 updating image from  '' to 'ubuntu-1804-bionic-v20210325'
2021/04/11 11:31:23 setting source image project to 'ubuntu-os-cloud'

The resulting Packer template looks as follows:

{
  "builders": [
    {
      "project_id": "my-project",
      "source_image": "ubuntu-1804-bionic-v20210325",
      "source_image_family": "ubuntu-1804-lts",
      "source_image_project_id": "ubuntu-os-cloud",
      "type": "googlecompute"
    }
  ]
}

As you can see, the version is updated and both the source image family and source image project are also added to the packer template. If your Packer template only has a source_image it works in the same way.

installation

To install the utility, either type:

go get github.com/binxio/gcp-hashicorp-packer-updater

Or download a pre-compiled binary from github.com/binxio.

conclusion

With this simple utility, you can keep the google source image version in your Packer template tied to a specific version and you can keep it up-to-date. The utility only works with JSON files, as these can be read and updated by a program. Once there is a HCL2 read/write library is available, I will update the utility to support that too.

Image by Vinson Tan ( 楊 祖 武 ) from Pixabay

Mark van Holsteijn is a senior software systems architect, and CTO of binx.io. He is passionate about removing waste in the software delivery process and keeping things clear and simple.
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